Solar cell element and solar cell module

ABSTRACT

A solar cell element comprises a semiconductor substrate, a passivation layer, and first to third electrodes. The passivation layer with first holes is located on the semiconductor substrate. The first electrode is located in each of the first holes and electrically connected to the semiconductor substrate. The second electrode is electrically connected to the first electrode and located on the passivation layer. The third electrode is electrically connected to the first electrode via the second electrode. The passivation layer includes a part where a ratio of an area occupied by the first holes in a first region adjacent to the third electrode is smaller than a ratio of an area occupied by the first holes in a second region located farther away from the third electrode in relation to the first region and having an area equal to an area of the first region in a perspective plan view.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a solar cell element and a solar cell module.

BACKGROUND ART

Known as one structure of solar cells (also referred to as solar cell elements) capable of increasing photoelectric conversion efficiency is a passivated emitter and rear cell (PERC) structure.

A solar cell element having the PERC structure comprises, for example, a passivation film on a rear surface of a silicon substrate. The solar cell element further comprises an electrode located to pass through the passivation film and a back surface electrode located on a substantially entire surface on a rear surface side of the silicon substrate.

SUMMARY

A solar cell element and a solar cell module are disclosed.

In one embodiment, a solar cell element comprises a semiconductor substrate, a passivation film, a first electrode, a second electrode, and one or more third electrodes. The passivation film is located on the semiconductor substrate and has a plurality of first holes. The first electrode is located in each of the plurality of first holes and electrically connected to the semiconductor substrate. The second electrode is electrically connected to the first electrode and located on the passivation film. The one or more third electrodes are electrically connected to the first electrode via the second electrode and located to linearly extend in a first direction. The passivation film includes a part where a ratio of an area occupied by the plurality of first holes in a first region adjacent to the one or more third electrodes is smaller than a ratio of an area occupied by the plurality of first holes in a second region located farther away from the one or more third electrodes in relation to the first region and having an area equal to an area of the first region in a perspective plan view.

In one embodiment, a solar cell module comprises one embodiment of the solar cell element and a connection tab being located to extend toward the first direction on the one or more third electrodes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a plan view showing one example of an external appearance of a solar cell element on a first surface side according to a first embodiment.

FIG. 2 illustrates a plan view showing one example of the external appearance of the solar cell element on a second surface side according to the first embodiment.

FIG. 3 illustrates an end view showing one example of an end surface of the solar cell element taken along a line III-III of FIG. 1 and FIG. 2.

FIG. 4 illustrates a perspective plan view showing a distribution of first holes in a passivation film according to the first embodiment.

FIG. 5(a) illustrates an enlarged end view schematically showing a portion near a first electrode of the solar cell element according to the first embodiment. FIG. 5(b) illustrates an enlarged plan view schematically showing the portion near the first electrode of the solar cell element according to the first embodiment.

FIG. 6(a) to FIG. 6(f) illustrate end views for describing a method of manufacturing the solar cell element according to the first embodiment.

FIG. 7(g) to FIG. 7(i) illustrate end views for describing a method of manufacturing the solar cell element according to the first embodiment.

FIG. 8(a) illustrates a plan view showing one example of an external appearance of a solar cell module on a first surface side according to the first embodiment. FIG. 8(b) illustrates a plan view showing one example of the external appearance of the solar cell module on a second surface side according to the first embodiment.

FIG. 9(a) illustrates a plan view showing one example of a solar cell element to which a connection tab is connected. FIG. 9(b) illustrates an end view showing one example of two solar cell elements connected to each other by a connection tab.

FIG. 10 illustrates a perspective plan view showing a relationship between the distribution of the first holes in the passivation film and a position of the connection tab according to the first embodiment.

FIG. 11 illustrates an exploded end view showing an exploded solar cell panel constituting the solar cell module according to the first embodiment.

FIG. 12 illustrates an end view showing one example of an end surface of a solar cell element according to a second embodiment.

DESCRIPTION OF EMBODIMENT(S)

Each embodiment is described hereinafter based on the drawings. In the drawings, components having similar configuration and function are denoted by the same reference symbols, and overlapping description will be omitted in the description below. The drawings are schematically illustrated, and therefore some of constituent elements are omitted in some cases. An XYZ coordinate system of a right-handed system is depicted in FIG. 1 to FIG. 12. In this XYZ coordinate system, a direction along one side of a solar cell element 10 is a +X direction, a direction along the other side intersecting with the one side is a +Y direction, and a direction perpendicular to both the +X direction and the +Y direction is a +Z direction.

1. First Embodiment 1-1. Solar Cell Element

As illustrated in FIG. 1 to FIG. 3, the solar cell element 10 includes a first surface 10 a located on a front side from which mainly light enters and a second surface 10 b located on an opposite side (back side) of the first surface 10 a.

A semiconductor substrate (also referred to as a substrate) 1 used for the solar cell element 10 also includes a first surface 1 a and a second surface 1 b located on an opposite side of the first surface 1 a in a similar manner. The substrate 1 includes a first semiconductor layer 2 as a semiconductor region of a first conductivity type (e.g., a p-type) and a second semiconductor layer 3 located on a first surface 1 a side of the first semiconductor layer 2 as a semiconductor region of a second conductivity type (e.g., an n-type).

One example of the solar cell element 10 in which a p-type polycrystalline silicon or a p-type monocrystalline silicon is used as the substrate 1 (or the first semiconductor layer 2) is described hereinafter.

The substrate 1 has a thickness of approximately 100 μm to 250 μm, for example. If the substrate 1 has a substantially quadrilateral shape formed of sides each ranging from approximately 150 mm to 200 mm in a plan view, a solar cell module 20 (refer to FIG. 8(a) and FIG. 8(b)) in which a large number of the solar cell elements 10 each having the substrate 1 are arrayed can be easily manufactured. However, a planar shape and size of the substrate 1 is not limited. Herein, for example, if a p-type impurity such as boron and/or gallium is contained as a dopant element in a silicon substrate, the first semiconductor layer 2 which is the p-type semiconductor region can be generated.

The second semiconductor layer 3 is located on the first semiconductor layer 2. The second semiconductor layer 3 is a semiconductor layer of the second conductivity type (an n-type in the first embodiment) opposite to the first conductivity type of the first semiconductor layer 2. A pn junction part is therefore formed between the first semiconductor layer 2 the second semiconductor layer 3. The second semiconductor layer 3 can be formed if an n-type impurity such as phosphorus as a dopant element is contained in the first surface 1 a side of the substrate 1, for example.

As illustrated in FIG. 3, the first surface 1 a in the substrate 1 includes a minute concave-convex structure (a texture) for reducing a reflection ratio of emitted light. Accordingly, a reflection of light can be reduced on the first surface 1 a side of the substrate 1. For example, a height of each protrusion of the texture ranges approximately from 0.1 μm to 10 μm. The distance between apexes of the adjacent protrusions of the texture ranges approximately from 0.1 μm to 20 μm for example.

The solar cell element 10 comprises an antireflection film 5 and a surface electrode 7 on the first surface 10 a side. The solar cell element 10 further comprises a back surface electrode 8 and a passivation film 4 on a second surface 10 b side.

The antireflection film 5 can reduce the reflection ratio of the light emitted to the first surface 10 a of the solar cell element 10. Accordingly, photoelectric conversion efficiency of the solar cell element 10 can be increased. The antireflection film 5 can be made up of an insulating film of silicon oxide, aluminum oxide, a silicon nitride or the like or a laminated film of those insulating films, for example. As a refractive index and a thickness of the antireflection film 5, for example, a refractive index and a thickness that allow light out of sunlight within such a wavelength range that is absorbed into the substrate 1 and can thus contribute to power generation to satisfy low reflection conditions may be adopted. If the antireflection film 5 of silicon nitride is formed by a plasma enhanced chemical vapor deposition (PECVD) method, for example, the antireflection film 5 having a refractive index of approximately from 1.8 to 2.5, and a thickness of approximately from 60 nm to 120 nm can be achieved.

As illustrated in FIG. 1, the surface electrode 7 is an electrode located on the first surface 1 a side of the substrate 1. The surface electrode 7 includes, for example, a plurality of bus bar electrodes 7 a (three in the example in FIG. 1) and a plurality of linear finger electrodes 7 b (forty in the example in FIG. 1).

The bus bar electrodes 7 a are linearly located in the Y direction in the example in FIG. 1. The bus bar electrodes 7 a are electrodes for outputting electricity obtained by a photoelectric conversion in the substrate 1 to an outer side of the solar cell element 10, for example. Each of the bus bar electrodes 7 a has a width of approximately 1 mm to 3 mm, for example. At least a part of the bus bar electrodes 7 a is electrically connected to the finger electrodes 7 b at a substantially right angle with the finger electrodes 7 b.

The finger electrodes 7 b can collect a carrier generated in accordance with incoming light in the substrate 1 and transmit the carrier to the bus bar electrodes 7 a. The finger electrodes 7 b are located to extend in the X direction. Each of the finger electrodes 7 b has a width of approximately 30 μm to 200 μm, for example. The plurality of the finger electrodes 7 b are located at an interval of approximately 1 mm to 3 mm therebetween. Herein, the surface electrode 7 may further include sub-finger electrodes 7 c located along the Y direction of a peripheral edge part 1Ed of the substrate 1 on the first surface 1 a side of the substrate 1, having a shape similar to that of the finger electrodes 7 b, thereby electrically connecting the plurality of the finger electrodes 7 b to each other, for example.

The surface electrode 7 can be formed by applying a conductive paste containing silver as a main component into a desired shape with screen printing or the like, and then performing sintering on the conductive paste, for example. Herein, the main component indicates a component whose content ratio to a whole component is equal to or larger than 50% by mass. Also in the description hereinafter, the main component indicates the meaning similar to the above description. The surface electrode 7 formed by performing the sintering on the conductive paste has a thickness of approximately 7 μm to 40 μm, for example.

The passivation film 4 is located on substantially the whole second surface 1 b of the substrate 1. The passivation film 4 has a plurality of first holes 9. Herein, each first hole 9 is located to pass through the passivation film 4 in a thickness direction. The passivation film 4 can reduce a defect level at an interface between the substrate 1 and the passivation film 4, and can reduce a recombination of minority carriers near the interface. The passivation film 4 can be made up of an insulating film of silicon oxide, aluminum oxide, a silicon nitride or the like or a laminated film of those insulating films, for example. The passivation film 4 has a thickness of approximately 6 nm to 100 nm, for example. In the first embodiment, if the first semiconductor layer 2 has the p-type conductivity, a film such as an aluminum oxide film, for example, having a negative fixed charge may be used as the passivation film 4. Herein, if the passivation film 4 having the negative fixed charge is adopted, for example, electrons, which are minority carriers, are brought away from the interface between the substrate 1 and the passivation film 4 due to an electric field effect of the passivation film 4. Accordingly, the recombination of minority carriers is reduced near the interface between the substrate 1 and the passivation film 4.

The passivation film 4 made of aluminum oxide can be formed on substantially the whole second surface 1 b by atomic layer deposition (ALD) method, for example. Furthermore, the first hole 9 can be formed in an optional position in the passivation film 4 by irradiating the passivation film 4 with a laser beam using a YAG (yttrium aluminum garnet) laser device.

As illustrated in FIG. 2 and FIG. 3, the back surface electrode 8 is an electrode located on a second surface 1 b side of the substrate 1. The back surface electrode 8 includes a first electrode 8 a, a second electrode 8 b, and a third electrode 8 c, for example.

The first electrode 8 a is located in the first hole 9 in the passivation film 4. As illustrated in FIG. 3, the first electrode 8 a is located in a through hole of each of the plurality of first holes 9. That is to say, there are the plurality of first electrodes 8 a. Each first electrode 8 a is electrically connected to the substrate 1. For example, one end of the first electrode 8 a is in direct contact with the second surface 1 b of the substrate 1. The one end needs to be located on a substrate 1 side of the first electrode 8 a in a passing-through direction of the first hole 9. The first electrode 8 a can thereby collect the carriers in the second surface 1 b of the substrate 1. The other one end of the first electrode 8 a is electrically connected to the second electrode 8 b. The other one end needs to be located on an opposite side of the substrate 1 in the first electrode 8 a in the passing-through direction of the first hole 9. The carriers collected by the first electrode 8 a can be thereby transmitted to the second electrode 8 b. Herein, a cross-sectional shape of the first electrode 8 a may be any of a circular shape, an oval shape, or a rectangular shape, or a band-like shape (linear shape), for example, in a perspective plan view of the second surface 10 b. The first electrode 8 a may have a diameter (or a width) of, for example, approximately 60 μm to 500 μm.

The second electrode 8 b is located on the passivation film 4. The second electrode 8 b is electrically connected to both the first electrode 8 a and the third electrode 8 c. The second electrode 8 b can transmit the carriers collected by the first electrode 8 a to the third electrode 8 c. Thus, the second electrode 8 b is formed on substantially the whole second surface 1 b except for a peripheral edge and a part of a region where the third electrode 8 c is formed in the second surface 1 b to cover almost all of the first electrodes 8 a, for example.

The first electrode 8 a and the second electrode 8 b can be formed in the following manner, for example. Firstly, a conductive paste containing aluminum as a main component is applied on the passivation film 4 having the first holes 9 by screen printing or the like. At this time, the conductive paste enters the first holes 9, thereby also being located on the passivation film 4. Then, the conductive paste is sintered to form the first electrode 8 a and the second electrode 8 b. Herein, a layer thickness of the first electrode 8 a is equal to that of the passivation film 4. The second electrode 8 b has a thickness of approximately 15 μm to 50 μm, for example.

Herein, if the first electrode 8 a is formed using a conductive paste containing aluminum, for example, a back surface field (BSF) layer 13 is formed in the substrate 1. For example, after the conductive paste containing aluminum is applied on the passivation film 4, the conductive paste is sintered with a predetermined temperature profile having a maximum temperature equal to or higher than a melting point of aluminum. The first electrode 8 a is thereby formed, and an interdiffusion of elements occurs between aluminum in the conductive paste and the substrate 1. As a result, the BSF layer 13 containing higher concentration of aluminum than that of the first semiconductor layer 2 is formed in the substrate 1. Herein, since aluminum can be a p-type dopant, the concentration of the dopant contained in the BSF layer 13 is higher than that of the dopant contained in the first semiconductor layer 2. As described above, the BSF layer 13 contains first conductivity type dopant elements at a higher concentration than that of first conductivity type dopant element in the first semiconductor layer 2. The BSF layer 13 forms an internal electric field on the second surface 1 b side of the substrate 1. Thus, the recombination of the minority carriers can be reduced near the surface of the second surface 1 b in the substrate 1. As a result, the photoelectric conversion efficiency of the solar cell element 10 is hardly reduced. The BSF layer 13 can be formed if dopant elements such as boron or aluminum are contained, through diffusion, in a surface layer portion on the second surface 1 b side of the substrate 1, for example. A concentration of the dopant elements contained in the first semiconductor layer 2 is set to approximately 5 ×10¹⁵ atoms/cm³ to 1×10¹⁷ atoms/cm³, for example. A concentration of the dopant elements contained in the BSF layer 13 is set to approximately 1×10¹⁸ atoms/cm³ to 5×10²¹ atoms/cm³, for example.

The third electrode 8 c is located on the second surface 1 b of the substrate 1. The third electrode 8 c is electrically connected to the first electrode 8 a via the second electrode 8 b. The third electrode 8 c is located in a position facing the bus bar electrodes 7 a with the substrate 1 therebetween. Herein, each of N or more (N indicates a natural number) third electrodes 8 c is located to linearly extend toward a first direction (the +Y direction in the example in FIG. 2). The third electrodes 8 c are electrodes for outputting electricity obtained by the photoelectric conversion in the substrate 1 to the outer side of the solar cell element 10, for example. The third electrodes 8 c are located on the passivation film 4 not to overlap with the first electrodes 8 a in a plan view, or linearly located in a state of passing through the passivation film 4. Each of the third electrodes 8 c has a thickness of approximately 5 μm to 30 μm and a width of approximately 1 mm to 7 mm, for example. Herein, the plurality of third electrodes 8 c may be located side by side toward a second direction (the +X direction in the example in FIG. 2) perpendicular to the first direction as illustrated in FIG. 2, for example. Accordingly, current generated by the photoelectric conversion in the substrate 1 can be dispersedly output to the outer side of the solar cell element 10, for example. As a result, a serial resistance component in the solar cell element 10 can be reduced.

Each third electrode 8 c may include a plurality of island shaped portions linearly arranged toward the +Y direction as illustrated in FIG. 2. Each third electrode 8 c may have a shape to be sequentially formed in a linear region located from an end on a −Y side to an end on a +Y side on the second surface 1 b of the substrate 1, similarly to the shape of the bus bar electrode 7 a. However, if the third electrode 8 c includes the plurality of island shaped portions, the first electrode 8 a or the passivation film 4 and the second electrode 8 b can be located between the plurality of island shaped portions in a perspective plan view of the second surface 10 b. Accordingly, the photoelectric conversion efficiency of the solar cell element 10 can be increased. The second electrode 8 b may overlap with a peripheral part of the third electrode 8 c, for example, in a perspective plan view of the second surface 10 b. The third electrode 8 c may include a rectangular main body of an electrode and a protruding part located to protrude from the main body, for example. In this case, if the protruding part is covered by the second electrode 8 b, the third electrode 8 c and the second electrode 8 b can be electrically connected to each other. If the third electrode 8 c contains silver or copper which can be soldered as a main component, a connection tab which is a ribbon-like connected conductor can be easily connected to the third electrode 8 c in a process of manufacturing a solar cell module. The third electrode 8 c can be formed by applying a conductive paste containing silver as a main component into a desired shape with screen printing or the like, and then performing sintering on the conductive paste, for example.

Next, a function of the solar cell element 10 according to the first embodiment is described. In the solar cell element 10 according to the first embodiment, the passivation film 4 includes a part where a ratio of an area occupied by the plurality of first holes 9 in a first region A1 is smaller than a ratio of an area occupied by the plurality of first holes 9 in a second region A2 in a perspective plan view as illustrated in FIG. 4. Herein, the first region A1 is a region adjacent to the third electrode 8 c in a perspective plan view. The second region A2 is a region located farther away from the third electrode 8 c in relation to the first region A1 and having an area equal to that of the first region A1 in a perspective plan view.

When the first electrode 8 a and the second electrode 8 b are formed by performing the sintering on the conductive paste containing a metal, a component in the substrate 1 (e.g., silicon) is diffused in the first electrode 8 a and the second electrode 8 b, for example. The component in the substrate 1 is diffused more easily as the thicknesses of the first electrode 8 a and the second electrode 8 b are smaller. If the component is diffused in such a manner, the metal component in the first electrode 8 a and the second electrode 8 b and the component in the substrate 1 react to each other, and a region having high electrical resistance (also referred to as a high resistance region) is formed near the first hole 9. Thus, in the solar cell element 10 according to the first embodiment, the plurality of first holes 9 are distributed so that there is the part where the ratio of the area occupied by the plurality of first holes 9 in the first region A1 is smaller than the ratio of the area occupied by the plurality of first holes 9 in the second region A2 in a perspective plan view of the second surface 10 b. Accordingly, a serial resistance component in an equivalent circuit in the solar cell element 10 according to the first embodiment can be reduced. As a result, the photoelectric conversion efficiency of the solar cell element 10 can be increased.

Particularly if there is the BSF layer 13 as described above, the semiconductor component such as silicon is diffused in the second electrode 8 b when the BSF layer 13 is formed in the substrate 1 as illustrated in FIG. 5(a). A part 8 bh containing an alloy of silicon and aluminum and having high electrical resistance (also referred to as a high resistance part) is thereby formed in the second electrode 8 b. The high resistance part 8 bh in the second electrode 8 b is larger than the first electrode 8 a. Thus, as illustrated in FIG. 5(b), a plane area of the high resistance part 8 bh is larger than that of the first hole 9 in a perspective plan view of the second surface 10 b. In the solar cell element 10, if an intensity distribution of received light is even, the carrier can be generated almost evenly by the photoelectric conversion except for a position where the surface electrode 7 is formed. However, a flow of the carrier is directed toward the third electrode 8 c for outputting the current. At this time, a current density shows a tendency to increase with a decreasing distance to the third electrode 8 c.

Thus, in the first embodiment, a contact area between the plurality of first electrodes 8 a and the second electrodes 8 b per unit area decreases with the decreasing distance to the third electrode 8 c in a perspective plan view of the second surface 10 b. That is to say, the passivation film 4 includes the part where the ratio of the area occupied by the plurality of first holes 9 per unit area decreases with the decreasing distance to the third electrode 8 c in a part between the adjacent third electrodes 8 c in a perspective plan view of the second surface 10 b. Assumed specifically is a case where the N third electrodes 8 c includes a primary third electrode 8 c 1, a secondary third electrode 8 c 2, and a tertiary third electrode 8 c 3 arranged from the +X side toward the −X side as illustrated in FIG. 2. In this case, in the passivation film 4, as illustrated in FIG. 4, the ratio of the area occupied by the plurality of first holes 9 decreases with the decreasing distance to the primary third electrode 8 c 1 or the secondary third electrode 8 c 2 in the part between the primary third electrode 8 c 1 and the secondary third electrode 8 c 2 adjacent to each other in a perspective plan view of the second surface 10 b. In the passivation film 4, the ratio of the area occupied by the plurality of first holes 9 decreases with the decreasing distance to the secondary third electrode 8 c 2 or the tertiary third electrode 8 c 3 in the part between the secondary third electrode 8 c 2 and the tertiary third electrode 8 c 3 adjacent to each other in a perspective plan view of the second surface 10 b. That is to say, there is a region where the contact area between the plurality of first electrodes 8 a and the second electrodes 8 b per unit area decreases with the decreasing distance to the third electrode 8 c in the part between the adjacent third electrodes 8 c in a perspective plan view of the second surface 10 b, for example. Accordingly, the ratio of the high resistance part 8 bh per unit area decreases in a region where the current density relatively increases, for example. As a result, the serial resistance component in the equivalent circuit in the solar cell element 10 can be reduced, for example. Accordingly, the photoelectric conversion efficiency of the solar cell element 10 can be increased.

Described hereinafter is a configuration example which can further increase the photoelectric conversion efficiency of the solar cell element 10.

As described above, as illustrated in FIG. 4, the passivation film 4 includes a part where the ratio of the area occupied by the plurality of first holes 9 in the first region A1 adjacent to the third electrode 8 c is smaller than the ratio of the area occupied by the plurality of first holes 9 in the second region A2 located farther away from the third electrode 8 c in relation to the first region A1 and having the area equal to that of the first region A1 in a perspective plan view.

In the solar cell element 10, for example, a region d1 is located between a region where the primary third electrode 8 c 1 is located and a region where the secondary third electrode 8 c 2 adjacent to the region of the primary third electrode 8 c 1 is located in a perspective plan view of the second surface 10 b. In the region d1, the carrier generated by the photoelectric conversion in the substrate 1 moves toward the third electrode 8 c located nearest in the ±X direction. Thus, in the region d1, the current density may increase from a central part of the region d1 in the +X direction toward a k1 direction (the +X direction) and a k2 direction (the −X direction). In contrast, as illustrated in FIG. 4, if the size of each first hole 9 is the same in a perspective plan view of the second surface 10 b, for example, a distance between centers of the adjacent first holes 9 is reduced to maximize the number of the first holes 9 per unit area near the central part of the region d1 in the +X direction. In other words, for example, the ratio of the area occupied by the plurality of first holes 9 per unit area is the largest near the central part of the region d1 in the +X direction in a perspective plan view of the second surface 10 b. For example, the distance between the centers of the adjacent first holes 9 is increased so that the first holes 9 are distributed sparsely in increments or in stages toward the k1 direction (the +X direction) and the k2 direction (the −X direction) from the central part of the region d1 in the +X direction as a boundary in the region d1 in a perspective plan view of the second surface 10 b. Accordingly, the serial resistance component in the equivalent circuit in the solar cell element 10 can be reduced, for example. As a result, the photoelectric conversion efficiency of the solar cell element 10 can be increased. Herein, in a perspective plan view of the second surface 10 b, for example, the description of “toward the k1 direction (the +X direction) in the region d1” indicates “closer to the region where the primary third electrode 8 c 1 is located in the region d1”. For example, in a perspective plan view of the second surface 10 b, the description of “toward the k2 direction (the −X direction) in the region d1” indicates “closer to the region where the secondary third electrode 8 c 2 is located in the region d1”.

A region d2 is located between a peripheral edge part (also referred to as a right peripheral edge part) 1EdR located in a +X direction side of the substrate 1 and a region where the primary third electrode 8 c 1 is located in a perspective plan view of the second surface 10 b, for example. In the region d2, the distance between the centers of the adjacent first holes 9 may be reduced to maximize the number of the first holes 9 per unit area on a right peripheral edge part 1EdR side, for example. That is to say, for example, the ratio of the area occupied by the plurality of first holes 9 per unit area may be the largest on the right peripheral edge part 1EdR side of the region d2 in a perspective plan view of the second surface 10 b. In this case, the distance between the centers of the adjacent first holes 9 may be increased so that the first holes 9 are distributed sparsely in increments or in stages toward a k4 direction (the −X direction) from the right peripheral edge part 1EdR side in a perspective plan view of the second surface 10 b, for example. Herein, for example, in a perspective plan view of the second surface 10 b, the description of “toward the k4 direction (the −X direction) from the right peripheral edge part 1EdR side in the region d2” indicates “closer to the region where the primary third electrode 8 c 1 is located in the region d2”.

Similarly, a region d3 is located between a peripheral edge part (also referred to as a left peripheral edge part) 1EdL located in a −X direction side of the substrate 1 and a region where the tertiary third electrode 8 c 3 is located in a perspective plan view of the second surface 10 b, for example. Also in the region d3, the distance between the centers of the adjacent first holes 9 may be reduced to maximize the number of the first holes 9 per unit area on a left peripheral edge part 1EdL side, for example. That is to say, for example, the ratio of the area occupied by the plurality of first holes 9 per unit area may be the largest on the left peripheral edge part 1EdL side of the region d3 in a perspective plan view of the second surface 10 b. In this case, the distance between the centers of the adjacent first holes 9 may be increased so that the first holes 9 are distributed sparsely in increments or in stages toward a k5 direction (the +X direction) from the left peripheral edge part 1EdL side in a perspective plan view of the second surface 10 b, for example. Herein, in a perspective plan view of the second surface 10 b, for example, the description of “toward the k5 direction (the +X direction) from the left peripheral edge part 1EdL side in the region d3” indicates “closer to the region where the tertiary third electrode 8 c 3 is located in the region d3”.

Furthermore, if the third electrode 8 c includes the plurality of island shaped portions, for example, the passivation film 4 may include a part where the ratio of the area occupied by the plurality of first holes 9 per unit area decreases with a decreasing distance to the island shaped portions in the +Y direction in a perspective plan view of the second surface 10 b. In other words, there may be a region where the contact area between the first electrodes 8 a and the second electrodes 8 b per unit area decreases with the decreasing distance to the island shaped portions in a perspective plan view of the second surface 10 b, for example. Herein, the connection tab connected to the third electrode 8 c is connected to the third electrode 8 c along the +Y direction (or the −Y direction). A direction of electricity from the solar cell element 10 to the connection tab is thereby the +Y direction (or the −Y direction). Thus, the distance between the centers of the adjacent first holes 9 may be increased so that the first holes 9 are distributed sparsely in increments or in stages toward the k3 direction (the +Y direction) in the region d1, for example. Herein, the k3 direction is a direction from an end d1 a side which is a side of the region d1 in the −Y direction toward an end d1 b side which is a side of the region d1 in the +Y direction located on an opposite side of an end d1 a. Accordingly, the serial resistance component in the equivalent circuit in the solar cell element 10 can be reduced, for example. As a result, the photoelectric conversion efficiency of the solar cell element 10 can be increased.

The passivation film 4 may include a part where the ratio of the area occupied by the plurality of first holes 9 per unit area decreases with a decreasing distance to the third electrode 8 c between both ends of the third electrode 8 c in a longitudinal direction and the peripheral edge part 1Ed of the substrate 1 in a perspective plan view of the second surface 10 b, for example. Assumed herein as illustrated in FIG. 2 is a case where the third electrode 8 c has a first end E1 on a side in the −Y direction and a second end E2 on a side opposite to the first end E1 (a side in the +Y direction) in the longitudinal direction (the ±Y direction herein). In this case, as illustrated in FIG. 4, the passivation film 4 may include a part where the ratio of the area occupied by the plurality of first holes 9 decreases with a decreasing distance to the third electrode 8 c between a region where the first end E1 is located and an upper peripheral edge part 1EdU in the longitudinal direction of the third electrode 8 c in a perspective plan view of the second surface 10 b, for example. Herein, the upper peripheral edge part 1EdU is a part located close to the first end E1 in the peripheral edge part 1Ed of the substrate 1. The passivation film 4 may include a part where the ratio of the area occupied by the plurality of first holes 9 decreases with a decreasing distance to the third electrode 8 c between a region where the second end E2 is located and a lower peripheral edge part 1EdB in the longitudinal direction of the third electrode 8 c in a perspective plan view of the second surface 10 b, for example. Herein, the lower peripheral edge part 1EdB is a part located close to the second end E2 in the peripheral edge part 1Ed of the substrate 1.

In another respect, the passivation film 4 may include a part where the ratio of the area occupied by the plurality of first holes 9 decreases with a decreasing distance to the third electrode 8 c between a first part En1 where the first end E1 is located and the upper peripheral edge part 1EdU in the longitudinal direction of the region where the third electrode 8 c is located in a perspective plan view of the second surface 10 b, for example. The passivation film 4 may include a part where the ratio of the area occupied by the plurality of first holes 9 decreases with a decreasing distance to the third electrode 8 c between a second part En2 where the second end E2 is located and the lower peripheral edge part 1EdB in the longitudinal direction of the region where the third electrode 8 c is located in a perspective plan view of the second surface 10 b, for example. In other words, there may be a region where the contact area between the first electrodes 8 a and the second electrodes 8 b per unit area decreases with the decreasing distance to the third electrode 8 c in a perspective plan view of the second surface 10 b, for example.

As illustrated in FIG. 4, for example, a region d4 is located between a peripheral edge part (an upper peripheral edge part) 1EdU located in a −Y direction side of the substrate 1 and a region where the secondary third electrode 8 c 2 is located in a perspective plan view of the second surface 10 b, for example. Also in the region d4, the distance between the centers of the adjacent first holes 9 may be decreased so that the first holes 9 are distributed sparsely in increments or in stages from an upper peripheral edge part 1EdU side toward a k6 direction (the +Y direction) directed to a region side where the secondary third electrode 8 c 2 is located, for example. As illustrated in FIG. 4, for example, the distance between the centers of the adjacent first holes 9 increases so that the first holes 9 are distributed sparsely in increments or in stages toward a k7 direction (the −Y direction) also in a region between a peripheral edge part (a lower peripheral edge part) 1EdB of the substrate 1 in the +Y direction and a region where the third electrode 8 c is located in a perspective plan view of the second surface 10 b. Accordingly, the serial resistance component in the equivalent circuit in the solar cell element 10 can be reduced. As a result, the photoelectric conversion efficiency of the solar cell element 10 can be increased.

As illustrated in FIG. 4, for example, the plurality of first holes 9 may be located to be evenly distributed in a region d5 between the peripheral edge part 1Ed of the substrate 1 and the end d1 b of the region d1 and a region d6 between the peripheral edge part 1Ed of the substrate 1 and the end of the region d2 in the +Y direction. However, for example, the first holes 9 may be distributed sparsely in increments or in stages with a decreasing distance to the second end E2 of the third electrode 8 c. Specifically, the plurality of first holes 9 may be distributed sparsely in increments or in stages in a direction close to a nearest end of the third electrode 8 c (also referred to as a k8 direction) in regions between the lower peripheral edge part 1EdB located in the peripheral edge part 1Ed of the substrate 1 in the +Y direction and the regions d1, d2, and d3, for example. Similarly, the plurality of first holes 9 may be distributed sparsely in increments or in stages in a direction close to a nearest end of the third electrode 8 c (the k8 direction) in regions between the upper peripheral edge part 1EdU located in the peripheral edge part 1Ed of the substrate 1 in the −Y direction and the regions d1, d2, and d3, for example.

In the solar cell element 10 in which a polycrystalline silicon substrate having approximately 150 mm to 160 mm is used, the contact area between the first electrodes 8 a and the second electrodes 8 b per unit area is set to a value described hereinafter in a repeated experiment performed by the inventors. The contact area in the central part of the region d1 in the +X direction in a part on the end d1 a side of the region d1 is set to approximately 6 mm²/cm² to 15 mm²/cm². The contact area in a part nearest to the third electrode 8 c in the k1 direction (the +X direction) or the k2 direction (the −X direction) in the part on the end d1 a side of the region d1 is set to approximately 2 mm²/cm² to 5.9 mm²/cm². The contact area in the central part of the region d1 in the +X direction in the part on the end d1 b side of the region d1 is set to approximately 2 mm²/cm² to 5.9 mm²/cm². The contact area in a part nearest to the third electrode 8 c in the k1 direction (the +X direction) or the k2 direction (the −X direction) in the part on the end d1 b side of the region d1 is set to approximately 0.1 mm²/cm² to 1.9 mm²/cm².

The contact area between the first electrodes 8 a and the second electrodes 8 b per unit area in the solar cell element 10 can be measured in the following manner. For example, firstly, the part on second surface 10 b side of the solar cell element 10 is ground with an abrasive paper or the like to remove the second electrode 8 b. The end of the first electrode 8 a being in contact with the second electrode 8 b is thereby exposed. Then, an area of the exposed end of the first electrode 8 a is measured using an optical microscope or the like. It is also applicable, for example, to immerse the solar cell element 10 into a hydrochloric acid solution having a concentration of approximately 5% to 30% by mass and dissolve the first electrode 8 a and the second electrode 8 b to expose the passivation film 4 made of aluminum oxide, and measure the area of the first hole 9 using an optical microscope or the like.

1-2. Method of Manufacturing Solar Cell Element

Next, each process of the method of manufacturing the solar cell element 10 is described.

Firstly, the substrate 1 is prepared as illustrated in FIG. 6(a). The substrate 1 may be made of a monocrystalline silicon or a polycrystalline silicon, for example. The substrate 1 is formed by an existing Czochralski (CZ) method, casting method or the like, for example. Described hereinafter is an example of using the p-type polycrystalline silicon substrate as the substrate 1. For example, an ingot of the polycrystalline silicon is prepared by the casting method herein. Electrical resistivity of the ingot may range from 1Ω·cm to 5Ω·cm, for example. Herein, boron may be added to the polycrystalline silicon as a dopant element, for example. Next, the ingot of the polycrystalline silicon is sliced using a wire saw device to obtain the plurality of substrates 1. The substrate 1 has a front surface and a back surface each having a square shape with sides of approximately 160 mm in length and a thickness of approximately 200 μm, for example. Subsequently, if a small amount of etching is performed on the whole front surface and back surface of the substrate 1 with a solution of sodium hydroxide (NaOH), potassium hydroxide (KOH), hydrofluoric-nitric acid or the like, for example, a mechanical damage layer and a contamination layer occurred in slicing the substrate 1 can be removed.

As illustrated in FIG. 6(b), a texture may be formed on the first surface 1 a of the substrate 1 to reduce a reflection of light. The texture can be formed by wet etching using an alkaline solution of NaOH and the like or an acid solution of hydrofluoric-nitric acid and the like, dry etching using reactive ion etching (RIE) method or the like, for example.

Next, as illustrated in FIG. 6(c), the n-type second semiconductor layer 3 is formed in a surface layer portion on the first surface 1 a side of the substrate 1 having the texture. The second semiconductor layer 3 can be formed by application thermal diffusion method, gas phase thermal diffusion method, or the like, for example. The application thermal diffusion method is, for example, a method in which a diphosphorus pentaoxide (P₂O₅) paste is applied on the first surface 1 a of the silicon substrate 1, and phosphorus is thermally diffused in the surface layer portion on the first surface 1 a side of the substrate 1. The gas phase thermal diffusion method is, for example, a method in which a phosphorus oxychloride (POCl₃) gas is used as a diffusion source of phosphorus. The second semiconductor layer 3 is formed to have a thickness of approximately 0.1 μm to 2 μm and a sheet resistance of approximately 40Ω/□ to 200Ω/□. Herein, in the gas phase thermal diffusion method, the substrate 1 is heat treated in an atmosphere of a diffused gas made of POCl₃ and the like at a temperature of approximately 600° C. to 800° C. for approximately 5 minutes to 30 minutes to form phosphorus silicate glass (also referred to as PSG) on the surface of the substrate 1, for example. The substrate 1 is then heat treated in an atmosphere of an inert gas such as argon or nitrogen at a high temperature of approximately 800° C. to 900° C. for approximately 10 minutes to 40 minutes, for example. Accordingly, phosphorus is diffused from the PSG to the surface layer portion of the substrate 1, and the second semiconductor layer 3 is thereby formed in the surface layer portion on the first surface 1 a side of the substrate 1.

If the second semiconductor layer 3 is also formed on the second surface 1 b side in the process of forming the second semiconductor layer 3, the second semiconductor layer 3 formed on the second surface 1 b side is removed by etching. The p-type first semiconductor layer 2 is thereby exposed on the second surface 1 b side of the substrate 1. At this time, the second semiconductor layer 3 formed on the second surface 1 b side is removed by immersing the second surface 1 b of the substrate 1 in a hydrofluoric-nitric acid solution, for example. Subsequently, the PSG adhered to the first surface 1 a side of the substrate 1 at the time of forming the second semiconductor layer 3 is removed by etching. At this time, the second semiconductor layer 3 formed on a side surface of the substrate 1 may also be removed.

Next, as illustrated in FIG. 6(d), the passivation film 4 made of aluminum oxide, for example, is formed on the first semiconductor layer 2 on the second surface 1 b side. ALD method, PECVD method or the like can be adopted as a method of forming the passivation film 4, for example. Herein, if the ALD method is adopted, a coverage rate (a coverage) by the passivation film 4 on the second surface 1 b of the substrate 1 is increased, for example. A passivation effect by the passivation film 4 can be thereby enhanced.

In forming the passivation film 4 by the ALD method, the substrate 1 in which the second semiconductor layer 3 has been formed is disposed in a chamber of a film formation apparatus firstly. Then, processes A to D described hereinafter are repeated several times in a state where the substrate 1 is heated at a temperature ranging from 100° C. to 250° C. The passivation film 4 made of aluminum oxide with a desired thickness can be thereby formed on the substrate 1. The following is contents of the processes A to D.

[Process A]

An aluminum material, such as trimethylaluminum (TMA), for formation of aluminum oxide is supplied on the substrate 1 in the chamber of the film formation apparatus along with a carrier gas such as an Ar gas or a nitrogen gas. The aluminum material is thereby absorbed onto an entire periphery of the substrate 1. A length of time to supply TMA may be approximately 15 to 3000 milliseconds, for example.

[Process B]

The inside of the chamber of the film formation apparatus is purified with a nitrogen gas. The aluminum material in the chamber is thereby removed. At this time, further removed is the aluminum material other than a constituent which is chemically absorbed at an atomic layer level in the aluminum material which is physically absorbed and chemically absorbed onto the substrate 1. Herein, a length of time for purifying the inside of the chamber with the nitrogen gas may be approximately one second to several tens of seconds, for example.

[Process C]

An oxidizer such as water or an ozone gas is supplied into the chamber of the film formation apparatus. At this time, the alkyl group contained in TMA is removed so that the OH group is substituted for the alkyl group. Accordingly, the atomic layer of aluminum oxide is formed on the substrate 1. A length of time for supply the oxidizer into the chamber may be, for example, approximately 500 to 1500 milliseconds. Herein, hydrogen atoms are easily included in the aluminum oxide film, which has been formed, by supplying the hydrogen atoms along with the oxidizer into the chamber.

[Process D]

The inside of the chamber of the film formation apparatus is purified with a nitrogen gas. The oxidizer in the chamber is thereby removed. At this time, the oxidizer which has not contributed to a reaction at the time of forming aluminum oxide at the atomic layer level on the substrate 1 is removed, for example. Herein, a length of time for purifying the inside of the chamber with the nitrogen gas may be approximately one second to several tens of seconds, for example.

Subsequently, the aluminum oxide film having a desired layer thickness of approximately 6 nm to 200 nm, for example, can be formed by repeating a series of processes of the process A to the process D several times.

Although the case of forming aluminum oxide using TMA as the aluminum material is described herein, the other material may be used as the aluminum material. Applicable is a material which has an appropriate steam pressure of 100 Pa or higher as a gas supply source and can be supplied to the inside of the chamber in a gas state at a material supply temperature which can be set to range from −20° C. to 120° C., for example. For example, triethylaluminum (TEA) or the like can be adopted as the other material. As described above, the passivation film 4 can also be formed on the entire periphery of the substrate 1 including the side surface of the substrate 1 in addition to the second surface 1 b of the first semiconductor layer 2 as the p-type semiconductor region by using the ALD method. In this case, it is applicable to form an acid-resisting layer or the like by application on the passivation film 4 formed on the second surface 1 b of the substrate 1, and subsequently removing the unnecessary passivation film 4 with hydrofluoric acid or the like by etching.

Next, as illustrated in FIG. 6(e), the antireflection film 5 including a silicon nitride film is formed on the first surface 1 a side of the substrate 1, for example. The antireflection film 5 can be formed using PECVD method, sputtering method or the like, for example. When the PECVD method is applied, the substrate 1 is previously heated at a higher temperature than a temperature in forming the film on the substrate 1, for example. Subsequently, a mixed gas of silane (SiH₄) and ammonia (NH₃) is diluted by nitrogen (N₂), and is then supplied to the heated substrate 1, for example. Then, the component of the mixed gas is plasmatized by glow discharge decomposition at a reaction pressure in the chamber within a range from 50 Pa to 200 Pa and deposited on the first surface 1 a, thereby forming the antireflection film 5, for example. Herein, a film formation temperature may range approximately from 350° C. to 650° C., for example. A frequency of a high-frequency power source necessary for the glow discharge may range approximately from 10 kHz to 500 kHz, for example. A flow rate of the gas supplied to the chamber is appropriately determined in accordance with a size of the chamber and the like. The flow rate of the gas supplied to the chamber may range from 150 sccm to 6000 sccm, for example. At this time, a ratio (=B/A) of the flow rate B of ammonia to the flow rate A of silane may be approximately 0.5 to 15, for example.

Next, the plurality of first holes 9 are formed in the passivation film 4 as illustrated in FIG. 6(f). Herein, for example, the plurality of first holes 9 can be formed in a pattern illustrated in FIG. 4 by irradiating the second surface 1 b side of the substrate 1 with a laser beam using a laser device. A neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with Q switch (laser beam wavelength 1064 nm), a second harmonic of the Nd:YAG laser (SHG, laser beam wavelength 532 nm) or the like can be used for the laser device. For example, if the second harmonic of the Nd:YAG laser with Q switch is used, a condition where an oscillating frequency is 10 kHz, an output ranges from 7 W to 10 W, and a beam diameter is approximately 100 μm can be adopted. Herein, for example, it is also applicable that the first hole 9 is not formed in a position where the third electrode 8 c is to be formed.

Next, as illustrated in FIG. 7(g) to FIG. 7(i), the surface electrode 7 (the bus bar electrode 7 a, the finger electrode 7 b, and the sub-finger electrode 7 c) and the back surface electrode 8 (the first electrode 8 a, the second electrode 8 b, and the third electrode 8 c) are formed in a manner described hereinafter.

First, as illustrated in FIG. 7(g), the surface electrode 7 is formed using a first paste 16. Adopted herein is a conductive paste containing a metal powder including silver as a main component, for example, as the first paste 16. The metal powder may be made up of a silver powder in which a main metal component has a particle diameter of approximately 0.05 μm to 20 μm or approximately 0.1 μm to 5 μm, for example. A contained amount of silver contained in the metal powder may be approximately 65% to 85% by mass of total mass of the conductive paste. The first paste 16 further contains an organic vehicle and a glass fit, for example. Herein, a concentration of the organic vehicle in the first paste 16 may be approximately 5% to 15% by mass of the total mass of the conductive paste, for example. A concentration of the glass frit in the first paste 16 may be approximately 0.05% to 10% by mass of the total mass of the conductive paste, for example. Herein, the first paste 16 is firstly applied on the first surface 1 a side of the substrate 1 using a screen printing to have a pattern illustrated in FIG. 1. Then, processing of evaporating a solvent at a predetermined temperature to dry the applied first paste 16, for example, is performed on the applied first paste 16.

Next, as illustrated in FIG. 7(h), the third electrode 8 c of the back surface electrode 8 is formed using a second paste 17. Adopted herein is a conductive paste containing a silver powder, an organic vehicle, and a glass frit as main components, for example, as the second paste 17. The second paste 17 may be similar to the first paste 16 described above. The screen printing method or the like, for example, can be adopted as a method of applying the second paste 17. Herein, processing of evaporating a solvent at a predetermined temperature to dry the second paste 17 is performed on the second paste 17 after applying the second paste 17 on the passivation film 4, for example.

Furthermore, as illustrated in FIG. 7(i), the first electrode 8 a and the second electrode 8 b are formed using a third paste 18. Adopted herein is a conductive paste containing a metal powder including aluminum as a main component, for example, as the third paste 18. The metal powder may be made up of an aluminum powder in which a main metal component has a particle diameter of approximately 0.05 μm to 20 μm or approximately 0.1 μm to 5 μm, for example. A contained amount of aluminum contained in the metal powder may be approximately 65% to 80% by mass of total mass of the conductive paste. The third paste 18 further contains an organic vehicle and a glass frit, for example. Herein, a concentration of the organic vehicle in the third paste 18 may be approximately 5% to 15% by mass of the total mass of the conductive paste, for example. A concentration of the glass frit in the third paste 18 may be approximately 0.05% to 10% by mass of the total mass of the conductive paste, for example. Herein, the third paste 18 is firstly applied on the second surface 1 b side of the substrate 1 to cover the first holes 9 which have been formed already. At this time, if the third paste 18 is applied on substantially an entire surface of an area on the second surface 1 b side of the substrate 1 where the third electrode 8 c is to be not formed, the inside of the first holes 9 can be filled with the third paste 18 without a rigorous alignment. The screen printing method or the like, for example, can be adopted as a method of applying the third paste 18. Processing of evaporating a solvent at a predetermined temperature to dry the applied third paste 18 may be performed on the applied third paste 18.

Subsequently, the substrate 1 on which the first paste 16, the second paste 17, and the third paste 18 have been applied is sintered in a baking furnace in a state that a maximum temperature of approximately 700° C. to 950° C. is kept for approximately several tens of seconds to several tens of minutes. Accordingly, each conductive paste (the first paste 16, the second paste 17, and the third paste 18) is sintered. Accordingly, as illustrated in FIG. 3, the surface electrode 7 (the bus bar electrode 7 a, the finger electrode 7 b, and the sub-finger electrode 7 c) and the back surface electrode 8 (the first electrode 8 a, the second electrode 8 b, and the third electrode 8 c) are formed. The first paste 16 passes through the antireflection film 5 at the time of the sintering. The surface electrode 7 is thereby formed to be connected to the n-type second semiconductor layer 3 on the first surface 1 a side of the substrate 1. The first electrode 8 a is formed by performing the sintering on the third paste 18 filled in the inside of the first hole 9. At this time, the BSF layer 13 is formed in a surface layer portion of the second surface 1 b of the substrate 1 in accordance with the formation of the first electrode 8 a. Furthermore, the second electrode 8 b is formed by performing the sintering on the third paste 18 applied on the second surface 1 b side of the substrate 1 to cover the first holes 9. Furthermore, the third electrode 8 c is formed by performing the sintering on the second paste 17. At this time, the third electrode 8 c may be formed on the passivation film 4 without second paste 17 passing through the passivation film 4 by the sintering, or the third electrode 8 c may be formed on the first semiconductor layer 2 with the second paste 17 passing through the passivation film 4 by the sintering. Herein, for example, a component of the glass frit in the second paste 17 is appropriately adjusted, thus it can be controlled whether or not the second paste 17 passes through the passivation film 4. For example, a glass frit of SiO₂—BiO₃—PbO system can be applied to the glass frit to make the second paste 17 pass through the passivation film 4. In the meanwhile, for example, a glass frit of B₂O₃—SiO₂—ZnO system can be applied to the glass frit not to make the second paste 17 pass through the passivation film 4.

1-3. Solar Cell Module

As illustrated in FIG. 8(a) and FIG. 8(b), the solar cell module 20 includes a solar cell panel 23 including the plurality of solar cell elements 10 and a frame 24 located on an outer peripheral part of the solar cell panel 23. The solar cell module 20 includes a first surface 20 a which is a surface which mainly receives light and a second surface 20 b corresponding to a back surface of the first surface 20 a. The solar cell module 20 includes a terminal box 25 on the second surface 20 b as illustrated in FIG. 8(b). An output cable 26 for supplying electrical power generated in the solar cell module 20 to an external circuit is wired to the terminal box 25.

The solar cell element 10 according to the first embodiment described above is applied to the solar cell element 10 constituting the solar cell module 20, for example. Herein, the solar cell elements 10 adjacent to each other in the solar cell module 20 are electrically connected to each other via the connection tab 22 as illustrated in FIG. 9(a) and FIG. 9(b). A metallic foil of copper or aluminum having a thickness of approximately 0.1 mm to 0.3 mm, for example, is applied to the connection tab 22. A solder coats a surface of the metallic foil, for example. The solder can be formed to have an average thickness of approximately 5 μm to 30 μm, for example, by plating or dipping. A width of the connection tab 22 may be equal to or smaller than that of the bus bar electrode 7 a of the solar cell element 10, for example. Accordingly, the connection tab 22 hardly blocks the solar cell element 10 from receiving the light. The connection tab 22 may be connected to substantially the entire surface of the bus bar electrode 7 a and the third electrode 8 c. Accordingly, the resistance component in the solar cell element 10 can be reduced. Herein, if the substrate 1 which has a front surface and a back surface each having substantially a square shape with sides of approximately 160 mm in length is used, for example, the connection tab 22 having a width of approximately 1 mm to 3 mm and a length of approximately 260 mm to 320 mm can be adopted.

As illustrated in FIG. 9(a), a first connection tab 22 a in the plurality of connection tabs 22 connected to one solar cell element 10 is soldered on the bus bar electrode 7 a on the first surface 10 a of the solar cell element 10. A second connection tab 22 b in the plurality of connection tabs 22 is soldered on the third electrode 8 c on the second surface 10 b of the solar cell element 10.

Herein, as illustrated in FIG. 9(b), the solar cell elements 10 (solar cell elements 10S and 10T) adjacent to each other are connected to each other via the connection tab 22. Specifically, the connection tab 22 includes, in a longitudinal direction, one end portion which is solder connected to the bus bar electrode 7 a on the first surface 10 a of the solar cell element 10S and the other end portion which is solder connected to the third electrode 8 c on the second surface 10 b of the solar cell element 10T, for example. Such a connection is repeatedly provided between the plurality of (approximately five to ten, for example) solar cell elements 10. That is to say, there is a solar cell string having the plurality of solar cell elements 10 linearly connected in series.

Herein, the solar cell module 20 includes the connection tab 22 located to extend toward the first direction on the third electrode 8 c, for example. As described above, the passivation film 4 includes the part where the ratio of the area occupied by the plurality of first holes 9 in the first region A1 adjacent to the third electrode 8 c is smaller than the ratio of the area occupied by the plurality of first holes 9 in the second region A2 located farther away from the third electrode 8 c in relation to the first region A1 and having the area equal to that of the first region A1 in a perspective plan view. In other words, the contact area between the first electrodes 8 a and the second electrodes 8 b per unit area decreases with the decreasing distance to the island shaped portions of the third electrode 8 c toward the first direction (the +Y direction), for example. For example, as illustrated in FIG. 10, the plurality of first holes 9 are most densely distributed on an end side located on the −Y direction side in the first direction (the +Y direction), and the plurality of first holes 9 are distributed sparsely toward the first direction in a perspective plan view of the passivation film 4. In contrast, if a direction of the connection tab 22 extending toward the adjacent solar cell element 10 is the first direction (a k9 direction) in the solar cell module 20, the current flows in the connection tab 22 in the first direction. If the plurality of first holes 9 have the distribution described in this case, for example, the serial resistance of the solar cell module 20 is reduced, and the photoelectric conversion efficiency of the solar cell module 20 can be increased.

As illustrated in FIG. 8(a), the solar cell module 20 comprises a plurality of (for example, approximately two to ten) solar cell strings described above. Herein, the plurality of solar cell strings are aligned substantially in parallel with each other at a predetermined interval of approximately 1 mm to 10 mm, for example. Each of the solar cell elements 10 located on each end of the plurality of solar cell strings are electrically connected to each other by a soldering of a lateral direction wiring 27, for example. Accordingly, the plurality of solar cell elements 10 constituting the plurality of solar cell strings are electrically connected to each other in series, for example. In the plurality of solar cell strings, an external leading wiring 32 (refer to FIG. 11) is connected to the two solar cell elements 10 located at the both ends and electrically connected to each other in series in the plurality of solar cell elements 10.

The solar cell module 20 includes a solar cell panel 23 in which a translucent substrate 28, a front surface side filler 29, the plurality of solar cell strings, a back surface side filler 30, and a back surface member 31 are laminated. The solar cell panel 23 is formed in the following manner, for example.

Firstly, the translucent substrate 28, the front surface side filler 29, the back surface side filler 30, and the back surface member 31 are prepared.

The translucent substrate 28 is made up of glass having translucency, for example. Herein, a super white glass, a toughened glass, a double-strength glass, or a heat reflecting glass, for example, having a thickness of approximately 3 mm to 5 mm is used for the glass.

Each of the front surface side filler 29 and the back surface side filler 30 is made of ethylene vinyl acetate copolymer (EVA) or polyvinyl butyral (PVB), for example. A sheet like member with a thickness of approximately 0.4 mm to 1 mm formed by a T-die and a push bench, for example, is used for the front surface side filler 29 and the back surface side filler 30.

The back surface member 31 has a role of reducing a water infiltration from outside, for example. A weather resistance fluorine contained resin sheet with an aluminum foil therein, polyethylene terephthalate (PET) on which alumina or silica is evaporated of the like, for example, is used for the back surface member 31. Herein, if the light entering from the second surface 20 b side of the solar cell module 20 is used for power generation, for example, the back surface member 31 may be made up of glass or a polycarbonate resin having translucency, for example.

Subsequently, as illustrated in FIG. 11, after the front surface side filler 29 is disposed on the translucent substrate 28, the plurality of solar cell strings to which the plurality of solar cell elements 10 are connected as described above, the back surface side filler 30, and the back surface member 31 are sequentially laminated to manufacture a laminated body.

Subsequently, the laminated body is set in a lamination device. Then, under reduced pressure, the laminated body is heated for, for example, approximately fifteen minutes to one hour at a temperature ranging from 100° C. to 200° C. with applying pressure, and the solar cell panel 23 can be thereby manufactured.

Then, as illustrated in FIG. 8(a) and FIG. 8(b), the frame 24 is attached to an outer peripheral part of the solar cell panel 23, and the terminal box 25 is attached to the back surface member 31 constituting the second surface 20 b as necessary, thereby the solar cell module 20 is completed.

2. Another Embodiment

The present disclosure is not limited to one embodiment described above, but many modifications and changes can be added within a scope of the present disclosure. For example, in performing the sintering for forming the electrode, the sintering for forming the first electrode 8 a and the second electrode 8 b may be performed separately after performing the sintering for forming the surface electrode 7 and the third electrode 8 c of the back surface electrode 8 which have the similar component.

2-1. Second Embodiment

For example, as illustrated in FIG. 12, a solar cell element 10A according to the second embodiment further comprising a protection film 11, based on the solar cell element 10 according to the first embodiment described above, may be adopted. In an example in FIG. 12, the protection film 11 is located between the passivation film 4 and the second electrode 8 b on the second surface 10 b side of the solar cell element 10A. The protection film 11 has a second hole 19 located on the first hole 9. Thus, the first hole 9 and the second hole 19 are communicated with each other to form one through hole. The first electrode 8 a is also located in the second hole 19 in addition to the inside of the first hole 9. In other words, the first electrode 8 a is located from the inside of the first hole 9 to the inside of the second hole 19.

The protection film 11 is made up of a silicon nitride film, a silicon oxide film or the like, for example. For example, a silicon nitride film having a film thickness of approximately 2 nm to 15 nm can be formed using PECVD method or sputtering method, for example. For example, a silicon oxide film having a film thickness of approximately 2 nm to 15 nm can be formed using PECVD method, for example. For example, in using the silicon nitride film as the protection film 11, if the film thickness of the protection film 11 is smaller than that of the passivation film 4, a negative fixed charge of aluminum oxide constituting the passivation film 4 becomes dominant over a positive fixed charge of silicon nitride constituting the protection film 11. Thus, the passivation effect of the passivation film 4 is hardly reduced.

The solar cell element 10A having the structure described above can be manufactured by forming the protection film 11 after the process of forming the passivation film 4 described above in the first embodiment, for example. Herein, for example, the protection film 11 can be formed on the substrate 1, on which the passivation film 4 has been formed on the second surface 1 b side, in the manner similar to the method of forming the antireflection film 5 described above, for example. Specifically, a mixed gas of silane and ammonia is diluted by nitrogen gas by PECVD method, and is then supplied on the substrate 1 in the chamber, for example. Then, the component of the mixed gas is plasmatized by glow discharge decomposition at a reaction pressure in the chamber within a range from 50 Pa to 200 Pa and deposited on the substrate 1, thereby being able to form the protection film 11.

The second hole 19 can be formed by a method similar to the method of forming the first hole 9 in the first embodiment described above, for example. Specifically, the first hole 9 and the second hole 19 can be formed at the same time by irradiating the protection film 11 with a laser beam, for example.

If there is the protection film 11, in forming the second electrode 8 b, for example, a transformation or breaking of the passivation film 4 due to a diffusion of aluminum hardly occurs at the time of performing the sintering on the third paste 18 containing aluminum as the main component. With this, a passivation effect of the passivation film 4 can be maintained.

EXPLANATION OF REFERENCE SIGNS

1: substrate (semiconductor substrate)

1 a: first surface

1 b: second surface

2: first semiconductor layer

3: second semiconductor layer

4: passivation film

5: antireflection film

7: surface electrode

7 a: bus bar electrode

7 b: finger electrode

7 c: sub-finger electrode

8: back surface electrode

8 b: first electrode

8 b: second electrode

8 bh: high resistance part in second electrode

8 c: third electrode

8 c 1: primary third electrode

8 c 2: secondary third electrode

8 c 3: tertiary third electrode

9: first hole

10: solar cell element

10 a: first surface

10 b: second surface

11: protection film

13: BSF layer

16: first paste

17: second paste

18: third paste

19: second hole

20: solar cell module

20 a: first surface

20 b: second surface

23: solar cell panel

24: frame

25: terminal box

26: output cable

27: lateral direction wiring

28: translucent substrate

29: front surface side filler

30: back surface side filler

31: back surface member

32: external leading wiring 

1. A solar cell element, comprising: a semiconductor substrate; a passivation layer being located on the semiconductor substrate and having a plurality of first holes; a first electrode being located in each of the plurality of first holes and electrically connected to the semiconductor substrate; a second electrode being electrically connected to the first electrode and located on the passivation layer; and one or more third electrodes being electrically connected to the first electrode via the second electrode and located to linearly extend in a first direction, wherein the passivation layer includes a part where a ratio of an area occupied by the plurality of first holes in a first region adjacent to the one or more third electrodes is smaller than a ratio of an area occupied by the plurality of first holes in a second region located farther away from the one or more third electrodes in relation to the first region and having an area equal to an area of the first region in a perspective plan view.
 2. The solar cell element according to claim 1, further comprising a protection layer being located between the passivation layer and the second electrode, and having a plurality of second holes being located on the plurality of first holes, wherein the first electrode is also located in each of the plurality of second hole in addition to an inside of each of the plurality of first holes.
 3. The solar cell element according to claim 1, wherein the one or more third electrodes include a plurality of third electrodes being located side by side toward a second direction perpendicular to the first direction.
 4. The solar cell element according to claim 1, wherein the one or more third electrodes include a primary third electrode and a secondary third electrode adjacent to each other, and the passivation layer includes a part where a ratio of an area occupied by the plurality of first holes decreases with a decreasing distance to the primary third electrode or the secondary third electrode in a part between the primary third electrode and the secondary third electrode in a perspective plan view.
 5. The solar cell element according to claim 1, wherein each of the one or more third electrodes includes a plurality of island shaped portions, and the passivation layer has a part where a ratio of an area occupied by the plurality of first holes toward the first direction decreases with a decreasing distance to at least one island shaped portion in the plurality of island shaped portions in a perspective plan view.
 6. The solar cell element according to claim 1, wherein each of the one or more third electrodes has a first end and a second end being located on a side opposite to the first end in the first direction, and the passivation layer includes a part where a ratio of an area occupied by the plurality of first holes decreases with a decreasing distance to the one or more third electrodes between the first end and a peripheral edge part being located on a side of the first end of the semiconductor substrate and between the second end and a peripheral edge part located on a side of the second end of the semiconductor substrate in the first direction in a perspective plan view.
 7. A solar cell module, comprising a solar cell element according to claim 1 and a connection tab being located to extend toward the first direction on the one or more third electrodes. 